I seem to remember that, not long after they were introduced, one unit exceeded 90mph on a test run somewhere between Leeds and York. It was in the railway press at the time but I don't think that it was on a public service. Of course, I could be mistaken and the unit I remember was a 155 but I don't think so as the 155s were sidelined for months because of a problem with the doors(?). This means that the 156s are (or were) capable of 90 but that they may now be limited by instruction rather than capability as I've been on one on a Barrow to Preston service which seemed to fly once on the WCML although this is very subjective and I only roughly timed a couple of quarter miles.